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• GoPro (MP4) video timestamp sync with precision of milliseconds

  3 février 2021, par Raphael Ottoni

  I need your help with a data sync problem... I m currently trying to sync my GoPro video with real world time (a.k.a my notebook). I manage to sync date and time of my notebook and my GoPro 3+ black perfectly. The problem is that when the GoPro save the files in disk it round up the milliseconds on the creation_time (the milliseconds is always 000000) . Thus, turning the perfect sync impossible. In attachment is a picture of the meta information (extracted by ffprobe) of the MP4 video.

  



  My question is : What I have to do, so the GoPro actually save the creation_time with precision of milliseconds ?

  



  Another small question : Looking at the attachment figure, we see the "timecode" which is a time synchronization data in the format of hours:minuts:seconds:frame. I was thinking that I could use the "frame" value to calculate the missing milliseconds value. If we take this attachment, as a example, we can see that the frame value is "36". Meaning that the millisecond that it started to record was the one associated with the 36th frame of the FPS (in this video : 60fps) value : Some thing like 1000/60 * 36 which is 600 milliseconds, thus the actual creation_time of this video would be : 2017-07-19T18:10:34.600

  



  Is this logic right ? it didn't work ! I don't know what else to do.

  



  P.S : I need this kind of time precision because I will sync the video frames with a external sensor data that is recorded at 11hz.

  



  Please Help

  



  

  



  update

  



  I forgot to mention, even if you check the original raw file information, inside the GoPro SSD card, using "stats" to read the creation time (see attachment) it still has the same timestamp without milliseconds.

  



  

  


• Is variable resolution possible in MPEG-4 or Matroska ?

  29 août 2020, par Chris_F

  It's become increasingly common for movies to contain sections with varying aspect ratios. For instance, the movie The Dark Knight is is sometime 16:9 full frame, and at other times 2.40:1 with letter boxing. This is fine when viewed on a 16:9 (or even 4:3) screen, but if you try to watch it on a 2.40:1 screen you will get simultaneous horizontal and vertical letterboxes. Extremely undesirable.

  


  Currently I use MPC-HC, which has a feature where it is able to analyze the video in real time, detect letter boxing, and dynamically crop the video. This works pretty well, but it's kind of an ugly solution. Are there any video formats that allow meta data like image resolution to change throughout the video ?

  


• Is there a way to handle discontinuities with FFMPEG ?

  16 avril 2020, par Dave Stein

  I am running ffmpeg like this, to get a screenshot from an HLS manifest :

  



  ffmpeg -i 'https://example.com/myfile.ism/manifest' -vframes 1 test.jpg -y

  



  There are times where there are gaps in the HLS manifest. When I run that command, it fails because it can't find a frame. Is there anything I can do to make it more resilient ? ie if it fails getting the time this very second, try the second before that ?

  



  When I watch the video in something like video.js, or even HLS directly in Safari, I see a frame regardless of gaps. It just jumps sometimes - I always see a frame.

  



  How would I be able to replicate that here such that the ffmpeg command will always return a frame ?